In general, a gasoline engine, in principle, uniformly mixes air and fuel prior to starting combustion and then ignites fuel using a spark plug to combust fuel, and a diesel engine, in principle, draws only air and compresses the air at a high compression ratio, and then injects fuel at high pressure into the air so as to allow fuel to reach self-ignition. In particular, regarding a general diesel engine, a method of allowing fuel injected from an injector to swirl in a combustion chamber (bowl) formed in a piston to mix fuel and air well and combust fuel is mainly used.
The combustion chamber of the diesel engine needs to be designed to maintain a state in which smoke does not become worse despite less smoke and a delay of injection timing. That is, the combustion chamber of the diesel engine needs to facilitate formation of a gaseous mixture by allowing the injected fuel to collide with a wall surface of the combustion chamber, and to inhibit fuel vapor from flowing to a squish region formed between a piston and a cylinder head while maintaining a swirl flow in the combustion chamber, thereby allowing air to actively flow.
The diesel engine injects fuel into the combustion chamber and mixes the fuel with drawn air at appropriate timing so as to facilitate combustion and exhibit engine performance, and in this case, fuel begins to be injected at the final time of the compression stroke, and fuel is mixed with air by the swirl flow in the combustion chamber and begins to be combusted from the final time of the compression stroke to the initial time of the explosion stroke, and thereafter, unburned smoke is mixed with air at the top of the piston by the squish flow and further combusted, thereby inhibiting smoke from being produced.
Therefore, in order to improve engine performance and reduce exhaust gas, a shape of the combustion chamber of the diesel engine needs to be optimized to optimally mix fuel and air in the combustion chamber.
FIGS. 1 and 2 are a top plan view and a cross-sectional view of a combustion chamber of a diesel engine in the related art, respectively, and a recessed combustion bowl 30, which allows a flow of fuel injected from an injector 70 to be a swirl flow and a squish flow at an upper side of a piston 10, is provided in the combustion chamber of the diesel engine. The piston 10 moves upward and downward while sliding along an inner circumferential surface of a cylinder block 20, and compresses or expands air in the combustion bowl 30, and at the same time, fuel injected from the injector 70 is mixed with the compressed air and then begins to be combusted.
Therefore, when high-pressure fuel is injected from the injector 70 in a state in which air drawn from an intake port is compressed by the upward movement of the piston 10, the fuel injected from the injector 70 induces a squish flow and a swirl flow in the combustion chamber formed in an upper surface of the piston 10, and is mixed with air that forms a turbulent flow.
However, according to the combustion chamber of the diesel engine in the related art, because the squish flow in which a gaseous mixture flows from the bowl to the squish region at an initial time of combustion cannot be concentrated toward an injection hole of the injector, a mixing rate of fuel and air deteriorates, and preservability of the swirl flow and intensity of the turbulent flow in the vicinity of the wall surface of the combustion chamber deteriorate, such that air in the squish region and the squish flow to be combusted are insufficient at the final time of combustion, thereby adversely affecting engine performance and reduction in exhaust gas.
The discussion above is merely provided for general background information and is not intended to be used as an aid in determining the scope of the claimed subject matter.